Different chainrings for Shimano 105 (1050 group)
09-02-18, 09:15 AM
#1
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Different chainrings for Shimano 105 (1050 group)
I have a 1987 Cannondale SR500 that I bought new way back then, and now am riding it regularly again after many years. It is performing very well, but due to living in a very hilly area, and my physical condition I am still finding some hills a challenge to the point where I have to get off the bike, and walk a bit to get up the hill. The bike is just geared too tall for me at this point.
The current gearing is 42/52 "Biopace" chainrings with the freewheel at 13, 15, 17, 19, 21, 28 (changed from 24 when I first bought it). So can I get existing chainrings to fit the crank for this 1050 crankset to at least make the gearing a bit more hill friendly? Say a 36/50 or thereabout? Thanks!
The current gearing is 42/52 "Biopace" chainrings with the freewheel at 13, 15, 17, 19, 21, 28 (changed from 24 when I first bought it). So can I get existing chainrings to fit the crank for this 1050 crankset to at least make the gearing a bit more hill friendly? Say a 36/50 or thereabout? Thanks!
09-02-18, 09:26 AM
#2
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In all likelihood, your crank has a 130mm BCD. For a crank like that the absolute smallest inner chainring size possible is 38 teeth these rings are very hard to find. The most common inner chainring size is 39 teeth. If you wish to go to a 50/36 or 50/34 you will need to buy a new crank
09-02-18, 09:31 AM
#3
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NO.
you have a 130 bolt circle crank most likely.. that is what you seek
from any aftermarket (round) chainrings.
to achieve any gear size smaller than 38t, the bolt circle on the cranks
must be smaller..
next smaller is a 110, low tooth count limit then 34t.
(commonly sold as 34-50 combinations) ..
...
you have a 130 bolt circle crank most likely.. that is what you seek
from any aftermarket (round) chainrings.
to achieve any gear size smaller than 38t, the bolt circle on the cranks
must be smaller..
next smaller is a 110, low tooth count limit then 34t.
(commonly sold as 34-50 combinations) ..
...
09-02-18, 09:40 AM
#4
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Thanks guys. So I could possibly go to a 39 inner ring, and if I want smaller, get a new crank? I wonder if a 39 would even be worth it at this point. Would a round smaller chainring be compatible with the oval, larger biopace 52 chainring?
09-02-18, 10:46 AM
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Here's a 1050 crank that I switched from 52/42 to 50/38. I don't need super-high gears, so dropping the size of the big ring kept the shifting nice:
That kind of a difference helps, but it won't work miracles. If you're having to walk a lot of hills with a 42/28 low gear, you'll probably want to start thinking about a different crankset.
That kind of a difference helps, but it won't work miracles. If you're having to walk a lot of hills with a 42/28 low gear, you'll probably want to start thinking about a different crankset.
09-02-18, 11:28 AM
#6
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Here's a 1050 crank that I switched from 52/42 to 50/38. I don't need super-high gears, so dropping the size of the big ring kept the shifting nice:
That kind of a difference helps, but it won't work miracles. If you're having to walk a lot of hills with a 42/28 low gear, you'll probably want to start thinking about a different crankset.
That kind of a difference helps, but it won't work miracles. If you're having to walk a lot of hills with a 42/28 low gear, you'll probably want to start thinking about a different crankset.
09-02-18, 11:56 AM
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Thanks, that's great info, and thanks for the pic. I don't have to walk a lot of hills, only the long, steep ones. So it isn't a huge problem, but annoying enough to make me want to change. I may do what you've done, and see if that is enough to make the difference. It may be, and if not I guess a different crank is in order. It may be time to just get a new, or newer bike also.
09-02-18, 11:56 AM
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https://www.treefortbikes.com/FSA-Ve...gaAh-kEALw_wcB
50/34t 9 speed with JIS square taper, should work ok. This is brand new, you could probably snag something cheaper on ebay
50/34t 9 speed with JIS square taper, should work ok. This is brand new, you could probably snag something cheaper on ebay
09-02-18, 12:30 PM
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What others have said. Dropping from a 42 to a 38 is a four tooth difference, or almost a 10% drop in ratio. So it's comparable to the shift from your 24 tooth cog to your 28 tooth biggest cog. Or it would be like having a 31 tooth big cog instead of a 28. If that's a big change to you, well, there you have it. More or less, although the more mathematically able will, I am sure, leap to other conclusions.
However, to me, that's just about the right difference in 'feel'. That's what I did on my Prologue, went from 52/42 to 50/38. Most of the other bikes in my collection have 50/34 compact cranks, but I can ride the Prologue with a 38/28 pretty much anyplace I'd ride a bike with a 34/28. Not everywhere, but pretty much.
If 10% doesn't sound like enough, then find a late 80's Deore crankset (a triple, but use only the two larger 110 bcd ring mounts) because the design aesthetic is most similar to your 105 group.
However, to me, that's just about the right difference in 'feel'. That's what I did on my Prologue, went from 52/42 to 50/38. Most of the other bikes in my collection have 50/34 compact cranks, but I can ride the Prologue with a 38/28 pretty much anyplace I'd ride a bike with a 34/28. Not everywhere, but pretty much.
If 10% doesn't sound like enough, then find a late 80's Deore crankset (a triple, but use only the two larger 110 bcd ring mounts) because the design aesthetic is most similar to your 105 group.
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09-02-18, 01:25 PM
#10
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Thanks again. I think I will try the 38/50 first, and the 10% drop may be just about right. I am working on getting in better riding shape, and now only the worst hills are by nemesis, and I am making it farther up, more, and more. I'd like to keep the rear derailleur as is if I can.
09-02-18, 02:13 PM
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Here's the 38T I used. It's the absolute smallest you can run on a 130BCD: https://www.amazon.com/Sugino-38t-13...dp/B001GSQITW/
09-02-18, 02:48 PM
#12
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^^^^^Thanks for that. I am going to give that a shot, and see if I can keep the 52t larger chainring, but sounds like I'd be better off eventually going to a 50 there.
09-02-18, 07:43 PM
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I'd recommend buying a replacement crank in "compact double" size, with a 110mm bolt circle diameter.
Buying 50 and 38 tooth chainrings won't get you much friendlier hill gearing, so why not spend a bit more (but not too much more) and buy a complete new crank with 48/34 or 50/34 teeth? That will drop your low gear twice as far from the current 42 small ring, plus it's usually cheaper to buy thigns as a package (crank with chainrings is cheaper than buying crank and rings separately; complete bike cheaper than buying frame and parts separately, etc.)
Buying 50 and 38 tooth chainrings won't get you much friendlier hill gearing, so why not spend a bit more (but not too much more) and buy a complete new crank with 48/34 or 50/34 teeth? That will drop your low gear twice as far from the current 42 small ring, plus it's usually cheaper to buy thigns as a package (crank with chainrings is cheaper than buying crank and rings separately; complete bike cheaper than buying frame and parts separately, etc.)
09-02-18, 09:02 PM
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If it is an '87 you probably have a 6 speed freewheel. I went from a 52/42 to a 46/38 but ultimately went with a triple setup as 46/38/30. A 50/34 won't buy you enough if you are having issues riding in a 42-28.
Your problem will be finding a freewheel that goes beyond a 28t which is why a triple crankset is a good option. The only decent freewheels I know of are older Suntour and Sachs-Aris LYXX. Some go up to 32t. The other issue will be replacing the rear derailleur with one that will go to a 32t, or a longer cage if you go with a triple crankset.
Your bike has 126mm dropouts so you can't swap out the rear wheel for a modern cassette. Don't fret though, I have '86 and '88 Cannondales and have no issues riding with a triple and a freewheel. I am running MTB rear derailleurs.
John
Your problem will be finding a freewheel that goes beyond a 28t which is why a triple crankset is a good option. The only decent freewheels I know of are older Suntour and Sachs-Aris LYXX. Some go up to 32t. The other issue will be replacing the rear derailleur with one that will go to a 32t, or a longer cage if you go with a triple crankset.
Your bike has 126mm dropouts so you can't swap out the rear wheel for a modern cassette. Don't fret though, I have '86 and '88 Cannondales and have no issues riding with a triple and a freewheel. I am running MTB rear derailleurs.
John
09-03-18, 06:57 AM
#15
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I'd recommend buying a replacement crank in "compact double" size, with a 110mm bolt circle diameter.
Buying 50 and 38 tooth chainrings won't get you much friendlier hill gearing, so why not spend a bit more (but not too much more) and buy a complete new crank with 48/34 or 50/34 teeth? That will drop your low gear twice as far from the current 42 small ring, plus it's usually cheaper to buy thigns as a package (crank with chainrings is cheaper than buying crank and rings separately; complete bike cheaper than buying frame and parts separately, etc.)
Buying 50 and 38 tooth chainrings won't get you much friendlier hill gearing, so why not spend a bit more (but not too much more) and buy a complete new crank with 48/34 or 50/34 teeth? That will drop your low gear twice as far from the current 42 small ring, plus it's usually cheaper to buy thigns as a package (crank with chainrings is cheaper than buying crank and rings separately; complete bike cheaper than buying frame and parts separately, etc.)
Yes, I have a six speed freewheel, and can't do much with it unless I change the rear derailleur. Jeez, I don't remember any of this being an issue thirty years, and 25 pounds ago.
09-14-18, 12:52 PM
#16
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I am going to go with the 38t inner chainring on the existing crank. Will this shift with my 52t biopace chainring, or do I need to go smaller to a 48, or 50? Also, will I need to shorten my chain to accommodate the smaller chainring? Thanks again.
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